from __future__ import with_statement

import logging
from logging.config import fileConfig

from alembic import context
from flask import current_app
from sqlalchemy import MetaData

from flask_state.conf.config import Config

USE_TWOPHASE = False

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# Interpret the config file for Python logging.
# This line sets up loggers basically.
fileConfig(config.config_file_name)
logger = logging.getLogger("alembic.env")

# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
config.set_main_option(
    "sqlalchemy.url",
    str(current_app.extensions["migrate"].db.engine.url).replace("%", "%%"),
)
bind_names = []


bind = Config.DEFAULT_BIND_SQLITE
if bind not in current_app.config.get("SQLALCHEMY_BINDS"):
    raise NameError("SQLALCHEMY_BINDS is missing `{}`".format(bind))
context.config.set_section_option(
    bind,
    "sqlalchemy.url",
    str(
        current_app.extensions["migrate"].db.get_engine(current_app, bind).url
    ).replace("%", "%%"),
)
bind_names.append(bind)

target_metadata = current_app.extensions["migrate"].db.metadata


# other values from the config, defined by the needs of env.py,
# can be acquired:
# my_important_option = config.get_main_option("my_important_option")
# ... etc.


def get_metadata(bind):
    """Return the metadata for a bind."""
    if bind == "":
        bind = None
    m = MetaData()
    for t in target_metadata.tables.values():
        if t.info.get("bind_key") == bind:
            t.tometadata(m)
    return m


def run_migrations_offline():
    """Run migrations in 'offline' mode.

    This configures the context with just a URL
    and not an Engine, though an Engine is acceptable
    here as well.  By skipping the Engine creation
    we don't even need a DBAPI to be available.

    Calls to context.execute() here emit the given string to the
    script output.

    """
    # for the --sql use case, run migrations for each URL into
    # individual files.

    engines = {}
    name = Config.DEFAULT_BIND_SQLITE
    engines[name] = rec = {}
    rec["url"] = context.config.get_section_option(name, "sqlalchemy.url")

    logger.info("Migrating database %s" % (name or "<default>"))
    file_ = "%s.sql" % name
    logger.info("Writing output to %s" % file_)
    with open(file_, "w") as buffer:
        context.configure(
            url=rec["url"],
            output_buffer=buffer,
            target_metadata=get_metadata(name),
            literal_binds=True,
        )
        with context.begin_transaction():
            context.run_migrations(engine_name=name)


def run_migrations_online():
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """

    # this callback is used to prevent an auto-migration from being generated
    # when there are no changes to the schema
    # reference: http://alembic.zzzcomputing.com/en/latest/cookbook.html
    def process_revision_directives(context, revision, directives):
        if getattr(config.cmd_opts, "autogenerate", False):
            script = directives[0]
            if len(script.upgrade_ops_list) >= len(bind_names) + 1:
                empty = True
                for upgrade_ops in script.upgrade_ops_list:
                    if not upgrade_ops.is_empty():
                        empty = False
                if empty:
                    directives[:] = []
                    logger.info("No changes in schema detected.")

    # for the direct-to-DB use case, start a transaction on all
    # engines, then run all migrations, then commit all transactions.
    engines = {}
    name = Config.DEFAULT_BIND_SQLITE
    engines[name] = rec = {}
    rec["engine"] = current_app.extensions["migrate"].db.get_engine(
        app=current_app, bind=name
    )

    engine = rec["engine"]
    rec["connection"] = conn = engine.connect()

    if USE_TWOPHASE:
        rec["transaction"] = conn.begin_twophase()
    else:
        rec["transaction"] = conn.begin()

    try:
        logger.info("Migrating database %s" % (name or "<default>"))
        context.configure(
            connection=rec["connection"],
            upgrade_token="%s_upgrades" % name,
            downgrade_token="%s_downgrades" % name,
            target_metadata=get_metadata(name),
            process_revision_directives=process_revision_directives,
            **current_app.extensions["migrate"].configure_args
        )
        context.run_migrations(engine_name=name)

        if USE_TWOPHASE:
            for rec in engines.values():
                rec["transaction"].prepare()

        for rec in engines.values():
            rec["transaction"].commit()
    except:  # noqa: E722
        for rec in engines.values():
            rec["transaction"].rollback()
        raise
    finally:
        for rec in engines.values():
            rec["connection"].close()


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()
